Russia and Syria have condemned the first US military strike against the Syrian regime, launched after a chemical weapons attack that killed dozens of civilians earlier in the week.

The Russian president, Vladimir Putin, denounced the strike on a Syrian airfield as "act of aggression" Friday and said it violated international law. Western leaders backed the US action, saying Syrian President Bashar al-Assad had brought it on himself.

On the orders of President Donald Trump, 59 Tomahawk cruise missiles were launched from US warships in the eastern Mediterranean. The missiles were directed at the Shayrat airfield, believed by the US to be the base for warplanes that carried out the chemical attack on a rebel-held town in Idlib on Tuesday.

Syria said six people were killed in the strike.

Key developments

Syrian airbase suffers "extensive damage" in strike. The UN Security Council is to meet Friday on Syria. Trump acted after dozens killed in chemical attack on Tuesday. Western allies offer strong backing, saying gas attack could not go unpunished. Russian President Vladimir Putin said US strike violated international law.

Trump said he ordered the operation after Tuesday's attack on the rebel-held town of Khan Sheikhoun that killed more than 80 people, including many children. Pictures from the aftermath of the attack, showing dead and injured children, shocked the world.

Western nations blamed the Syrian regime for the attack. But Russia said it did not believe the Syrian government held any chemical weapons.

Putin denounced the US action as "aggression against a sovereign state in violation of the norms of international law under a far-fetched pretext." He said the strikes "dealt a serious blow to Russian-US relations" and that their aim was to distract from the civilian deaths from coalition airstrikes in Iraq, a statement from his press office said.

Russian Foreign Minister Sergey Lavrov accused the United States of seeking a pretext for regime change. "I am particularly disappointed by the way this damages US-Russia relations," he said, but added that he didn't think it would "lead to an irreversible situation."

Syrian President Bashar al-Assad said the United States had carried out an "unjust and unabashed assault" against Syria which "shows nothing but short-sightedness, a narrowness of vision and a blindness to political and military realities."

He also said the attack had increased the regime's resolve to "crush" terrorists in Syria -- the term it uses for all opposition forces.

A statement from Syria's general military command said the strikes caused "extensive material damage" and undermined counterterror operations by the Syrian army. The operation "makes the United States of America a partner of ISIS, Nusra Front and other terrorist organizations who -- since the first day of this unjust war on Syria -- have been attacking Syrian army positions and Syrian military bases."

Syrian TV aired footage of the aftermath of the strike that showed smoke still rising up from the base.

The strike was the first direct military action taken by the US against the Assad regime since the start of the country's six-year civil war. It represents a substantial escalation of the US military campaign in the region.

Pentagon: 'Severe damage'

Trump announced the strikes in a brief statement to reporters at his Mar-a-Lago resort, saying there was "no doubt" that Syria had used chemical weapons in the attack on Khan Sheikhoun on Tuesday. "Years of previous attempts at changing Assad's behavior have all failed and failed very dramatically," he said.

The Pentagon said the strike, which began at 8:40 p.m. ET Thursday (3:40 a.m. local time Friday), targeted aircraft, storage facilities and other logistical materials.

An initial battle damage assessment from the strikes was that 58 of the 59 missiles "severely degraded or destroyed" their intended targets, according to a US defense official.

The US military gave the Russian military one hour's notice of the strikes, according to a senior US official. US military operations in Syria have been temporarily "adjusted" to ensure the protection of US forces on the ground, the official said. On any given day there could be up to 1,250 US troops inside Syria fighting ISIS, according to US officials.

Support from US allies

The strikes were supported by US allies, who also called for renewed efforts to find a political solution to the crisis. Turkey, a key regional player and partner in the fight against ISIS, said it considered the US action "a positive response to the Assad regime's war crimes," Turkish presidential spokesman Ibrahim Kalin said in a statement.

French President François Hollande and German Chancellor Angela Merkel said in a joint statement that they were given prior notice of the US operation. "Assad is entirely responsible for the development of the situation. His constant use of chemical weapons and his massive crimes must not go unpunished," they said.

"France and Germany will continue their efforts along with their partners throughout the United Nations framework in order to punish in the most appropriate way the criminal acts related to the use of chemical weapons, that are prohibited by all treaties."

"We fully support what the Americans have done," UK Defence Secretary Michael Fallon told the BBC, adding that the strike was "limited and wholly appropriate."

European Council President Donald Tusk also gave his backing to the US action, tweeting: "US strikes show needed resolve against barbaric chemical attacks. EU will work with the US to end brutality in Syria."

NATO Secretary General Jens Stoltenberg said the Syrian regime "bears the full responsibility for this development," adding that any use of chemical weapons "is unacceptable, cannot go unanswered, and those responsible must be held accountable."

Chinese foreign ministry spokeswoman Hua Chunying did not explicitly mention the US military strike in remarks to reporters but said China "noted the recent developments in Syria" and that it "always opposes the use of force in international affairs."

She also condemned the "recent chemical weapon attack in Syria" and called for an independent UN investigation.

Iran's Foreign Minister Javad Zarif tweeted that the United States had resorted to military force over "bogus" chemical weapons allegations. Iran is a major regional player whose forces have helped to bolster the Assad regime.

The UN Security Council is to meet Friday to discuss Syria, according to the US Mission to the United Nations.

The 15 members of the Security Council failed Thursday night to reach agreement on a a new draft resolution against the Syrian government circulated by US, UK and French diplomats following Tuesday's chemical attack. Russia has repeatedly vetoed past UN Security Council resolutions on Syria.

'Dangerous episode'

Matthew Chance, CNN's senior international correspondent based in Moscow, said the latest strikes "are an immensely dangerous episode in the relationship between Russia and the United States, not least because they potentially bring into contact Russian forces who are on the ground in Syria and the US forces."

Russia was warned of the attack before it took place. Nevertheless, Chance pointed out, Russia did not choose to use surface-to-air missiles systems in place in Syria that are "fully capable of intercepting cruise missiles if they so choose to" which, he said, "implies a degree of tacit Russian consent to the strikes."

In the wake of the strike, Russia said it was suspending use of a communications channel aimed at minimizing risks of in-flight incidents between the US-led coalition fighting ISIS in Syria and Russian aircraft. US military spokesman Col. John Dorrain said the "deconfliction channel" had been effective and urged its continued use.

The Russian Defense Ministry also announced plans to bolster the effectiveness of its air defense system in Syria.